Device for the continuous withdrawal of a granular solid



Dec. 9, 1969 AGNERAY ETAL 3,482,881

DEVICE FOR THE CONTINUOUS WITHDRAWAL OF A GRANULAR SOLID Filed April 26, 1968 2 Sheets-Sheet l HG. l

Dec. 9, 1969 1.. AGNERAY ETAL 3,482,881

DEVICE FOR THE CONTINUOUS WITHDRAWAL OF A GRANULAR SOLID Filed April 26, 1968 2 Sheets-Sheet 2 United States Patent U.S. Cl. 30242 3 Claims ABSTRACT OF THE DISCLOSURE A device for the continuous withdrawal of a granular solid from a pressurized enclosure comprises a gas-extraction box placed around a tube of small diameter through which a granular product is intended to flow under gravity between two chambers maintained at different pressures, a communication being provided between the box and the tube by way of holes formed in the tube wall. In order to recycle gases towards the chamber which is maintained at a higher pressure, the gas-extraction box is connected to a loop system which comprises a fan and a by-pass duct fitted with a flow-regulating valve. The valve is controlled so as to maintain within the tube section located between the extraction box and the lower-pressure chamher a pressure drop which corresponds to a zero rate of flow of gases within said tube section.

This invention relates to a device for withdrawing a granular solid from a pressurized enclosure without permitting any escape of gas, said granular product being caused to flow within said enclosure between two chambers at different pressures.

In conventional plants in which the transfer of solid products is carried out in this manner, provision is usually made for lock-chambers with valves, shutters of the rotating vane type or any equivalent mechanical components which serve to control the delivery of the product considered. Unless special precautions are taken, such mechanical components are called upon to work in contact with dust particles which are mainly the consequence of destroyed grains. Depending on the nature of the granular product being processed, said dust particles can be highly abrasive and are thus particularly liable to cause damage to the mechanisms employed. Moreover, depending on the pressure distribution within the enclosure, the flow of product is usually accompanied by a cocurrent or countercurrent gas flow which it may prove desirable to eliminate entirely.

The aim of the present invention is to provide a device whereby dust particles and gases can be completely removed from the path of the granular product without introducing any mechanical apparatus which would be liable to disturb the flow of said product.

Accordingly, said device is characterized in that it comprises a gas-extraction box adapted to surround a tube of small diameter through which the granular product is intended to flow under gravity between two chambers at diiierent pressures and adapted to communicate with the interior of said tube by way of holes formed in the tube wall, said box being connected to a loop system for recycling gases towards the chamber which is at the highest pressure and comprising a fan and a by-pass duct fitted with a flow-regulating valve, said valve being controlled so as to maintain within the tube section located between said box and the chamber which is at the lowest pressure a pressure drop corresponding to a zero rate of How of gases within said tube section.

As an advantageous feature, the valve for regulating the gas flow is controlled automatically by means of at detecting unit of the pressure transducer type which is associated with a regulating apparatus.

The complementary description which now follows illustrates two examples of practical application of the present invention which are given without any implied limitation.

In the accompanying drawings:

FIG. 1 is a diagrammatic sectional view of the withdrawal device under consideration which is primarily suited to the case of a flow of granular product which takes place from a high-pressure chamber towards a lowpressure chamber;

FIG. 2 is a diagrammatic sectional view of the same device which is modified to satisfy the case in which the flow of the granular product takes place from a lowpressure chamber towards a high-pressure chamber.

Identical reference numerals have been adopted in these figures for the purpose of designating components which are either similar or perform similar functions.

In the example of FIG. 1, a granular product 1 consisting of beads of silica having a diameter of the order of 1 mm. is caused to flow under gravity between two chambers 2 and 3 between which is maintained a pressure difference .of the order of 0.5 bar, for example, the pressure within the chamber 2 being higher than the pressure within the chamber 3. The two chambers are interconnected by means of a tube 4 which has a small diameter of the order of 30 mm. The extremity of said tube penetrates into the chamber 3 and opens into a sleeve 5 which forms a seating for a valve disc 6, said disc being actuated from the exterior of the chamber by means of a hand-wheel 7 so as to permit the outflow of the product 1.

Taking into account the pressure difference which exists between the chambers 2 and 3, the flow of the granular product is accompanied by a gas escape from the highpressure vessel to the low-pressure vessel; the device in accordance with the present invention makes it possible to reduce this gas escape to zero without disturbing the flow of the solid. To this end, said device comprises a casing or box 9 which surrounds the tube 4 substantially in the central region thereof and defines an internal space 10' which communicates with the interior of the tube 4 by means of small holes such as the hole 11 which are pierced in the tube wall in order to prevent the grains of the product from adhering to said wall. The box 9 is joined by means of a branch-pipe 12 to a recycling loop system 13, the intended function of which is to ensure that all the gases which accompany the granular product are returned in the direction of the high-pressure chamber 2.

To this end, at the outlet of the branch-pipe 12, the gas which is extracted from the box 9 is passed first through a filter 14 then into a duct 15 in which is mounted a fan 16 whose delivery outlet is directly connected to the chamber 2 by means of a second duct 17. A pipe 18 is mounted as a bypass across the fan 16 so as to provide a connection between the ducts 15 and 17. Said pipe 18 is fitted with a regulating valve 19' whereby the gas stream which passes through the loop 13 can be adjusted to a suitable rate of flow. To this end, the valve 19 is automatically controlled by means of a differential pressure transducer 20 which continuously measures by means of the pipes 21 and 22 the pressure difference which exists between the duct 15 on the one hand and the interior of the low-pressure chamber 3. The indications given by the transducer 20 are transmitted in the form of electric signals via a lead wire 23 to a regulator 24 which in turn delivers via the lead wire 25 a signal which serves to actuate the valve 19. By means of a suitable adjustment of the device, the flow of gas which is recycled through the loop 13 by means of the fan 16 is so adjusted that it reducesthe rate of flow of gas or of dust particles to zero in that portion of the tube 4 which is located between the box 9 and the chamber 3, said flow rate being precisely zero when the pressure which prevails within the chamber 3 is slightly higher than the pressure within the box 9 by a value equal to the pressure drop which would be obtained if the same gas were to pass within the tube 4 at the rate of flow of the granular solid. The differential transducer 20 therefore makes it possible to control and to act on the valve 19 in such a manner that the pressure difference between the duct and the chamber 3 is continuously maintained at the corresponding value of pressure drop.

In the example described above, the device can be put into operation irrespective of the pressure difference between the chambers 2 and 3 inasmuch as the gas flow assists the flow of the granular product which takes place cocurrentwise. However, in the embodiment shown by way of example in FIG. 2, the reverse arrangement is adopted in the case of the chambers 2 and 3 between which the granular product 1 flows. In this alternative form of construction, the chamber 2 is in fact at a lower pressure than that of the chamber 3 which, in this case, is the high-pressure chamber. But in this example, the pressure difference is necessarily limited inasmuch as the flow of product takes place countercurrent to the gas stream and this latter could fiuidize the granular product in the event of an excessive difference in pressure; by way of example, the pressure difference between the chambers 2 and 3 is of the order of 0.1 bar.

In the second embodiment now under consideration, the recycling loop 13 which comprises the fan 16 and the regulating valve 19 is mounted between the box 9 which is mounted in the central region of the tube 4 and the chamber 3 whilst the differential transducer 20 measures the pressure difference between the duct 15 and the chamber 2. In this case, the regulating valve 19 is actuated in such a manner as to maintain a pressure which is slightly higher within the box 9 than the pressure which exists within the chamber 2, the pressure difference being equal to the pressure drop corresponding to the flow rate which would be obtained if the gas were to pass through the tube 4 between the box 9 and the chamber 2.

Whatever form of construction may be adopted, the device which is thus provided makes it possible to carry out the continuous extraction of gases entrained by a granular product, the-operation ofsaid device being unattended by the least danger of destruction of the product considered or of disturbance of the product flow. Moreover, the very simple design and rugged construction of the device permits operation without difficulty at high temperature and at high pressure, even in highly corrosive media.

It is to be understood that the invention is not limited in any sense to the examples of construction as hereinabove described and as illustrated in the accompanying drawings but extends to all alternative forms.

What we claim is:

1. A device for the continuous withdrawal of a granular solid from a pressurized enclosure, characterized in that it comprises a gas-extraction box adapted to surround a tube of small diameter through which the granular product is intended to flow under gravity between two chambers at different pressures and also adapted to communicate with the interior of said tube by way of holes formed in the tube wall, said box being connected to a loop system for recycling gases towards the chamber which is at the highest pressure and comprising a fan and a bypass ductfitted with a flow-regulating valve, said valve being controlled so as to maintain within the tube section located between said box and the chamber which is at the lowest pressure a pressure drop corresponding to a zero rate of flow of gases within said tube section.

2. A device in accordance with claim 1, characterized in that the valve for regulating the gas fiow is controlled automatically by means of a detecting unit of the pressure transducer type which is associated with a regulating apparatus.

3. A device in accordance with claim 1, characterized in that the recycling loop is provided with a filter placed downstream of the extraction box.

References Cited UNITED STATES PATENTS 10/1959 Brooks 302-42 4/1965 Savage 302-42 US. Cl. X.R. 30253 

